Abstract: Magnetic Stratigraphy and Tectonic Rotation of the Middle-Upper Miocene Caliente Formation, Ventura County, California
McCARDEL, KRISTEN, DONALD R. PROTHERO, and ERIN L. WILSON
The Caliente Formation, in the Cuyama Badlands of northern Ventura County, California, contains a sequence of non-marine strata which span the late Hemingfordian, Barstovian, Clarendonian, and early Hemphillian land mammal "ages" (18-8 Ma), and also K-Ar dated volcanics. Paleomagnetic analysis of over 3000 samples from three sections (Dry Canyon, Apache Canyon, Sequence Canyon) showed that the remanence is held in hematite, and passes a reversal test for stability. These strata rest on a block within Transverse Range-San Andreas region that has been tectonically rotated since the early Miocene. The older strata (18 to 11 Ma) are rotated from 38 degrees plus or minus 23 degrees (18 Ma) to 37 degrees plus or minus 13 degrees (11 Ma) clockwise, but show no progressive rotational trends during this 7-million-year span. About 15 degrees of rotation apparently took place between 9 and 11 Ma (an interval missing the in Caliente Formation due to an unconformity), because all strata between 8 and 1.7 Ma are rotated about 23 degrees plus or minus 7 degrees clockwise. Rotation to the present orientation apparently took place since 1.7 Ma (Ellis et al., 1993).
The polarity patterns of the late Hemingfordian to Clarendonian section in Dry Canyon is correlated with Chrons C5Dr to C5r (18-11 Ma). Apache Canyon contains a thick early-late Clarendonian sequence correlated with Chrons C5An to C5r (12.5-,1 Ma), and Sequence Canyon contains a late Clarendonian-early Hemphillian sequence correlated with Chrons C4Ar to C4r (9-8 Ma). Chron C5n is apparently missing in all three sections. As in the Tejon Hills, the early/late Clarendonian boundary occurs in Chron C5r (11.5 Ma), contrary to results from the Ricardo Group in Red Rock Canyon, where it occurs in Chron C5n (11.0 Ma).
Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California